Hazardous contaminant emissions have become environmental issues of increasing concern because of the dangers posed to human health. For instance, coal-fired power plants and medical waste incineration are major sources of human activity related mercury emission into the atmosphere.
It is estimated that there are 48 tons of mercury emitted from coal-fired power plants in the United States annually. One DOE-Energy Information Administration annual energy outlook projected that coal consumption for electricity generation will increase from 976 million tons in 2002 to 1,477 million tons in 2025 as the utilization of coal-fired generation capacity increases. However, mercury emission control regulations have not been rigorously enforced for coal-fired power plants. A major reason is a lack of effective control technologies available at a reasonable cost, especially for elemental mercury control.
A technology currently in use for controlling elemental mercury as well as oxidized mercury is activated carbon injection (ACI). The ACI process involves injecting activated carbon powder into a flue gas stream and using a fabric filter or electrostatic precipitator to collect the activated carbon powder that has sorbed mercury. ACI technologies generally require a high C:Hg ratio to achieve the desired mercury removal level (>90%), which results in a high portion cost for sorbent material. The high C:Hg ratio indicates that ACI does not utilize the mercury sorption capacity of carbon powder efficiently.
An activated carbon packed bed can reach high mercury removal levels with more effective utilization of sorbent material. However, a typical powder or pellet packed bed has a very high pressure drop, which significantly reduces energy efficiency. Further, these fixed beds are generally an interruptive technology because they require frequent replacement of the sorbent material depending on the sorption capacity.
Activated carbon honeycombs disclosed in US 2007/0261557 may be utilized to achieve high removal levels of contaminants such as toxic metals. The inventors have now discovered new materials for flow-through sorbents, such as honeycombs, which are described herein.